Internal combustion engine are energy transforming mechanisms used by the vast majority of automotive vehicles, and comprise basically two main parts, namely: one or more engine head and the engine block. At the base of the head (s) are located combustion chambers (on Diesel engines in general the combustion chambers are arranged on the pistons heads) and on the engine block are located the cylinders and the crankshaft assembly. The crankshaft is composed by pistons, rods and crankshaft.
The engine converts produced by the combustion of the mixture (fuel and air) in the combustion chambers into mechanical energy capable of causing the wheels to turn.
Since the power required to move the automobile comes from the burning of the air/fuel mixture in the combustion chamber, and in order to ensure a homogeneous combustion, without burning oil, and still prevent the excessive passage of gases from the cylinder to the crankcase, it is necessary to use rings for providing good sealing of the clearance existing between the piston and the cylinder wall.
On most present-day internal combustion engines that operate according to the Otto and Diesel cycles, one uses three rings, two of which are compression rings and one is the oil control ring (scraper). The compression rings have the function of preventing passage of the gases from combustion into the crankshaft and the oil ring has the function of scraping the excess oil from the cylinder wall and return it to the crankshaft, controlling the oil-film thickness, so that the functioning of the engine will take place within the premises of the design and operation.
The oil scraping ring may be of one, two or three parts. The present solution has been developed in the form of a three-piece ring, which, as a general rule, has a first upper annular segment and a second lower annular segment, associated to an expanding intermediate element, which presses in a controlled manner the upper and lower segments against the cylinder wall. The force exerted by the expanding element, which is nothing else than a resilient element, is calculated so that the oil film on the cylinder wall will have the desired thickness.
At present, the need for greater thermal efficiency and specific power of the engines, markedly due to the limits of emission of pollutants and consumption of fuel and lubricating oil, have led to an increase in the thermal stresses and mechanical to which the internal components of the engines are subjected, among which are the oil scraping rings. Thus, in some more recent applications, the reduction of the durability of these components has been considerable, bringing about improvements.
The Japanese patent JP 5306461 relates to a sliding member whatever for use on an internal combustion engine, to which one applies a high-hardness TiCN coating, by the CVD process.
The coating is applied at a temperature of about 500° C.-600° C. with application of a gaseous mixture of TiCl4, H2, CH4 and N2, heating up to the plasma phase and evaporation up to the formation of a high-hardness film (between 2500 and 3000 Vickers) of 2 μm-20 μm.
This document, however, does not mention the formation of a tungsten carbide coating or the application thereof to oil scraping ring.
The Japanese prior-art document JP 3801250 relates to a 2-part oil-scraping ring, on which the external surface receives a coating applied by PVD or CVD. More specifically, one applies a coating by PVD or CVD to a geometrically specified surface, having a chamfered, angled or inclined surface, parallel to its internal circumference and with width between 0.15 mm and 0.3 mm.
This document, however, does not mention the formation of a tungsten carbide coating or even the application thereof to three-piece oil scrapers.
Document JP 06235462 relates to a three-piece combined ring, wherein the upper and lower annular segments receive the application of a TiCN coating of high hardness, by the CVD process, with thickness ranging from 3 μm to 15 μm, on its internal side surface and a chrome nitride coating ranging from 5 μm to 50 μm, applied by the ion-plating process onto its external side surface.
This document, however, does not mention the formation of a tungsten carbide coating or even the deposition thereof onto the ring expanding element.
European patent document EP 1686295 relates to a three-piece oil ring, on which the scraping element comprises the protrusions for association of the annular segments of austenitic stainless steel subjected to a nitriding treatment at a temperature of 470° C. or higher, so as to form a nitride layer of 10 to 60 microns. Alternatively, a coating (resin) layer is formed on at least one surface of the expander facing the surfaces of the annular segments or else on the surfaces of the annular segments that interact with the spacer.
This document, however, does not mention the formation of a tungsten carbide coating by CVD or even the deposition thereof onto the ring expanding element.
The patent document U.S. Pat. No. 5,718,437 relates to a three-piece oil ring where the upper and lower annular segments are made from martensitic stainless steel and receive a nitriding treatment. The expanding element, in turn, has a nitriding layer, onto which one applies a chrome nitride coating, formed by the ion-plating process on the circumferential outer surface of the part.
This document, however, does not mention the formation of a tungsten carbide coating by CVD or even the deposition thereof onto the ring expanding element.
The prior-art document BRPI 0516273-4 relates to a material resistant to wear, erosion and chemically resistant containing carbon-bound tungsten, the carbon being present in an amount ranging from 0.01% by weight to 0.097% by weigh of the total weight. The material preferably comprises a metallic tungsten matrix with tungsten carbide nanoparticles having particle size not larger than 50 nanometers, preferably not larger than 10 nanometers. The material is optionally also bonded to fluorine, the fluorine being present in an amount ranging from 0.01% by weight to 0.4% by weigh of the total weight.
This document, however, does not mention the formation of a tungsten carbide coating with deposition thereof onto an oil ring of an engine.
Finally, document BRPI 9917267-4 relates to a tungsten carbide alloy with addition of fluorine by up to 0.5% by weight and the fluorocarbon compositions. These alloys may be produced from a new chemical deposition process (CVD), in which tungsten hexachloride gases and gases containing carbon and hydrogen are used.
A specific feature of said process is the previous thermal activation of the carbon-containing gas. The tungsten carbide coating is applied onto the component whose strength one intends to increase.
Analogously, this document does not mention the formation of a tungsten carbide coating deposited on an engine oil ring.
In view of the aforesaid, a three-piece oil scraping ring whose expander and/or upper and lower annular segments is coated by means of the chemical deposition process (CVD), rendering the resulting ring high durability and maintaining its manufacture costs acceptable, has not been developed so far.